Ribbon cartridge

Abstract: The present invention relates to a ribbon cartridge comprising a housing (1) with an upper and a lower half, a ribbon (4) received in said housing, a driving means (7) comprising two driving gears (5,6) for driving said ribbon (4) said driving gears rotatably supported in the housing and in engagement with each other for transporting the ribbon (4) inbetween the driving gears. Specifically, the housing is provided with a bearing means (8) for supporting a first one of said driving gears (6) at a circumferential surface thereof in the middle of the height of said driving gear (6), so as to allow self-alignment of the driving gears with each other by adjustment movements other than a rotation around the axis of rotation.

Description: The present invention relates to a ribbon cartridge comprising a housing having a bottom half and a top half, a ribbon received in said housing, a driving means for driving said ribbon, said driving means having a first cylindrical driving gear and a second cylindrical driving gear, both being rotatably supported in said housing, said first driving gear being driven by said second driving gear, said driving gears being in engagement with each other for transporting the ribbon between said driving gears, bearing means for supporting the first driving gear at a circumferential groove in the middle of its height to allow self-alignment of said driving gear with the second driving gear by adjustment movements other than a rotation around the axis of rotation. Ribbon cartridges containing a ribbon which is normally inked nylon fabric or carbon coated film are nowadays widely used in computer printers, typewriters, cash registers and other impact printing machines which transfer the printing agent, namely the ink or the carbon, to the printing medium in accordance with the printing mechanism of the printer. The ribbon is normally an endless loop which is transported in and out of the cartridges continuously to allow the printing mechanism to print on a fresh portion of the ribbon to provide clear print images such as text, graphics, etc. From DE 31 38 828 C2 a conventional ribbon cartridge is known, which has a drive system consisting of two driving gears for transporting the ribbon. The driving gears are rotatably supported in a two-part housing and are in engagement with each other for transporting the ribbon in between said driving gears. The driving gears are pivoted on both the bottom half and the top half of the housing, so that their axis of rotation is fixed relative to the housing and therefore relative to each other when the two housing halves have been assembled. Since those driving gears are usually low-cost gears made of plastic, problems arise owing to the fixed axis of the driving gears. The pressure on the contacting surfaces of the teeth meshing with each other is not constant over a contacting length in axial direction of the driving gears, so that the ribbon transported in-between the two driving gears is caused to climb towards the top half of the housing or to slide downwards towards the bottom half of the housing what results in the ribbon being folded or twisted. Thus, the quality of printing can be reduced or even worse the drive system can be jammed or the ribbon may be damaged. A ribbon cartridge of the type as mentioned at the beginning is known from US-A-4,636,097. According to this known ribbon cartridge, the driven gear is held by a lever which is mounted on a pivot of the cartridge housing to allow self-alignment with the driving gear. Similarly, EP-A-0 428 123 discloses a driven gear which is held by a carriage. This carriage is pivotally mounted on a base wall of the cartridge housing. Furthermore, the carriage is provided with a fork serving as bearing means for the driven gear. In these two known cartridges, the driven gears in a ribbon advancing gear set are mounted on a swing lever to allow self-alignment with a driving gear. Even though rather complicated, this support structure has been considered necessary because on the one hand the axis of the gears in a ribbon advancing gear set have to be kept parallel in order to avoid clamping of the ribbon and, on the other hand, at least one roller has to be movable in a direction substantially perpendicular to said axis to prevent blocking of ribbon advancement between the rollers. In view of these drawbacks, the problem to be solved by the present invention is the simplification of the making of a ribbon cartridge and, in particular, of the support structure of the driven gear in a ribbon advancing gear set, thereby preventing the risk of causing band jam in the ribbon advancing gear set. This technical problem is solved by a ribbon cartridge of the type defined in the preamble portion of claim 1, wherein the bearing means is integrally formed with the bottom half of the housing while a self-alignment clearance is provided between the bearing means and the first driving gear. Accordingly, swing levers are no longer needed to prevent band jam. Moreover, the bearing of the driving gear provides equal pressure on both the top portion and the bottom portion of the teeth meshing with each other. Thus, the driving gears drive the ribbon more precisely without the problem of the ribbon climbing to the top or sliding to the bottom so that the ribbon is not folded or twisted. According to a preferred embodiment of the present invention the bearing means is a supporting protrusion extending towards said first driving gear in parallel with the bottom wall of said bottom half at a certain height thereabove and having an arcuate recess receiving said first driving gear. Thus, no additional part for supporting the driving gear is necessary, what reduces the costs of assembling the ribbon cartridge. Moreover, the driving gear nestles in the arcuate recess of the supporting protrusion, so that it can smoothly rotate and mesh with the other driving gear. Preferably the supporting protrusion extends from a supporting wall which is integral with and perpendicular to the bottom wall of the bottom half and has a curved shape following partially the circumference of the first driving gear. That reduces the self-supporting length of the supporting protrusion and reduces the maximum load on said supporting protrusion, since the momentum owing to leverage is small, so that the supporting protrusion can be thin. In a preferred embodiment of the present invention, the first driving gear is provided with a circumferential groove, the centre shaft of which is in engagement with said supporting protrusion. The driving gear is thereby precisely located and on the other hand the tooth tips of the driving gear are not worn off by the supporting protrusion. In this respect it is advantageous that the portion of the supporting protrusion delimiting the arcuate recess has a thickness in axial direction greater than the thickness of a body portion of said supporting protrusion, because a contact surface of the supporting protrusion contacting the driving gear is increased and thereby the wear and tear rate of both the supporting protrusion and the driving gear is reduced. Thus the life of the drive mechanism is extended. The aforementioned thickness in axial direction is still small enough to provide a clearance between the supporting protrusion and the groove to allow self-alignment of the first driving gear with the second driving gear by adjustment movements in particular around an axis perpendicular to the axis of rotation of the driving gears and thereby to produce equilibrium pressure along the contact line between the teeth meshing with each other. In accordance with a preferred embodiment of the present invention, a rejector finger extends essentially tangentially to the circumference of the first driving gear to prevent the ribbon from coiling around said first driving gear. Preferrably a lateral edge of the supporting protrusion embodies said rejector finger and extends essentially tangentially to the circumference of said first driving gear. As a result, the ribbon cannot stick up on the driving gear and is reliably transported inbetween the two driving gears. The second driving gear is, according to a preferred embodiment rotatably supported by the bottom half and the top half of the housing by means of a pivot bearing. Either the driving gear or the bottom half and/or the top half is provided with a circular protrusion to engage with a recess or opening in either the bottom half and/or the top half or in the second driving gear. Such a pivot bearing fixes the axis of rotation of the second driving gear in a very simple way which reduces the costs of the ribbon cartridge. That is specially advantageous because the second driving gear is connected to a driving mechanism of the printer or the typewriter, so that it is convenient that its position is fixed relative to the ribbon cartridge. In order to feed the ribbon manually and to take up the slack on the ribbon when installing the cartridge to printers and typewriters, the second driving gear is in a preferred embodiment provided with a turning knob extending through a hole in the top half of the housing. The turning knob is fitted in said hole in the top half and thereby serves at the same time as pivot bearing for the second driving gear. A preferred embodiment of the present invention shows a rejector arm extending essentially tangentially to the circumference of the second driving gear to prevent the ribbon from coiling around said second driving gear in a manner similiar to the above-described rejector finger associated with the first driving gear. The second driving gear is therefore provided with a circumferential groove from which the rejector arm integrally formed with the bottom half of the housing extends substantially tangentially to the bottom of said groove. In order to allow the supporting protrusion to be moulded in one piece with the bottom half, a first opening is formed according to a preferred embodiment in the bottom wall of the bottom half below the supporting protrusion, which opening is, shaped substantially correspondingly to the shape of the supporting protrusion. A mould for moulding the bottom half of the housing can therefore be simple, since no movable core is necessary for moulding the supporting protrusion in parallel with the bottom wall of the bottom half. Preferably, a second opening is correspondingly formed in the bottom wall of the bottom half below the rejector arm. Said second opening is shaped substantially correspondingly to the shape of the rejector arm according to a preferred embodiment of the present invention. Accordingly, the mould needs no movable core for moulding the rejector arm. In accordance with a preferred embodiment of the present invention, the top half and the bottom half of the housing are provided with positioning pins and positioning holes for connecting and positioning the top half and the bottom half relative to each other. By means of said positioning pins and positioning holes the assemblage of the ribbon cartridge is very convenient and quick, and moreover, the two halves can be positioned very exactly relative to each other, which is important because the second driving gear is rotatably supported by both the bottom half and the top half. Preferrably, the positioning pins are integrally formed with the top half or the bottom half, so that they can be moulded together with the top half or the bottom half and no further assembling step is necessary. Hereinafter, the present invention is illustrated and explained in greater detail by a preferred embodiment in conjunction with the accompanying drawings, wherein: Figure 1 shows in an overall isometric view a ribbon cartridge according to an embodiment of the present invention. Figure 2 shows in perspective the location and assembly of driving gears and a ribbon in a cartridge housing according to the embodiment of figure 1. Figure 3 shows a top view of the assembly of the driving gears supported in the housing according to the embodiment of figure 1. Figure 4 shows a section view A-A of figure 3. Figure 5 shows a back wall of the embodiment of figure 1, 2, 3, 4 in a back view. Figure 6 shows a front view of a bottom half of the cartridge housing according to the embodiment of figure 1. Figure 7 shows a top view of the bottom half as shown in figure 6. Figure 8 shows a bottom half as shown in figures 6 and 7 in a rear view. Figure 9 shows a bottom view of a bottom half as shown in Figures 6 to 8. Figure 10 shows a side view of the bottom half as shown in figures 6 to 9. Figure 11 shows a front view of a top half of the housing of the ribbon cartridge according to the embodiment of figure 1. Figure 12 shows a bottom view of the top half as shown in figure 11. Figure 13 shows a rear view of the top half as shown in figures 11 and 12. Figure 14 shows a top half as shown in figures 11 to 13 in a top view. Figure 15 shows a side view of a top half as shown in figures 11 to 14. Referring to figures 1 and 2, a driving means 7 of a ribbon cartridge according to the present invention is received in a bottom half 2 of a housing 1. The driving means 7, comprises a first driving gear 6 and a second driving gear 5, which are in engagement with each other. A ribbon 4 is transported in and out of the housing 1 in order to feed a printing mechanism of a printer or a typewriter which are not shown with a fresh portion of the ribbon 4 to provide clear print images. The ribbon 4 is transported inbetween the first driving gear 6 and the second driving gear 5 in a direction leading into a holding space 21 in which the ribbon 4 is arranged in loops. The first driving gear 6 is therefore rotated clockwise while the second driving gear 5 is rotated counterclockwise. It is to be noted, however, that the rotary direction depends on the side on which the driving means 7 is provided. If the driving means 7 is provided on the opposite side of the holding space 21, the first and second driving gears 6, 5 are rotated in the opposite rotary direction. The second driving element 5 is, as may be best seen in figures 3 and 4, supported by both the bottom half 2 and the top half 3 of the housing 1 to enable it to maintain its alignment at a fixed vertical axis. At the bottom, the second driving gear 5 is provided with a pivot which is received in an opening 23 in the bottom half 2 of the housing 1. On its upper side, the second driving gear 5 is provided with a turning knob 18 extending through a hole 25 in the top half 3 of the housing 1. The turning knob 18 is snugly fitted in said hole 25 in the top half 3 of the housing 1 so that the turning knob 18 serves as a pivot bearing on the upper side of the second driving gear 5. To serve its actual purpose the turning knob 18 is used for feeding the ribbon 4 manually to take up the slack on the ribbon 4 when installing the cartridge to a printing machine. The first driving gear 6 which is driven by the second driving gear 5 is supported by the bottom half 2 of the housing 1. As may be best seen in figures 3 and 4, a supporting protrusion 8 is integrally formed with the bottom half 2 of the housing 1. Said protrusion 8 extends from a supporting wall 9 towards said first driving gear 6 in parallel with the bottom wall 10 of the bottom half 2 at a certain height thereabove and has an arcuate recess 11 which receives the first driving gear 6. The first driving gear 6 has therefore a circumferential groove 12, the centre shaft 24 of which is in engagement with the recess 11 of the supporting protrusion 8. The groove 12 is located in the middle of the height of the first driving gear 6, so that the pressure on the contact surfaces of the meshing teeth of the first driving gear 6 and the second driving gear 5 is equal at the bottom portion close to the bottom wall 10 and at the top portion of the teeth close to the top half 3 to prevent the ribbon 4 from climbing towards the top half 3 or slipping towards the bottom half 2 of the housing 1 what would result in the ribbon 4 being folded or twisted. As may be best seen in figure 4, the supporting protrusion 8 has a portion 13 delimiting the arcuate recess 11, which portion 13 has a thickness in axial direction greater than the thickness of a body portion 14. The increased thickness of the portion 13 provides an increase in the contact surface of the supporting protrusion 8 and the first driving gear 6 to reduce the wear and tear of both the supporting protrusion 8 and the first driving gear 6, thus extending the life of the drive mechanism. In order to allow adjustment movements other than the rotation around the axis of rotation, there is clearance between the supporting protrusion 8 and the first driving gear 6, so that the first driving gear 6 may self-align with the second driving gear 5 which is supported with the fixed axis of rotation relative to the housing 1. The self-alignment of the first driving gear 6 compensates any manufacturing inaccuracy and enables the top and bottom layer of the contact surface of the first driving gear 6 to be engaged with the second driving element 5 with equilibrium pressure. Thus, the ribbon 4 can be transported more precisely without the problem of the ribbon 4 climbing towards the top or slipping down towards the bottom of the housing 1. Referring to figure 3, the supporting protrusion 8 is shaped in such a way that a lateral edge 15 serves as a rejector finger and extends essentially tangentially to the circumference of said first driving gear 6. Said lateral edge is in fact tangential to an imaginary circumference which is smaller in diameter than the circumference of the first driving gear 6 defined by the tooth tips, so the lateral edge 15 separates the ribbon 4 from the first driving gear 6 and prevents the ribbon 4 from coiling around said first driving gear 6. Correspondingly a rejector arm 17 associated with the second driving gear 5 extends essentially tangentially to a circumference of the second driving gear 5. The second driving gear 5 is therefore provided with a circumferential groove 16 from which the rejector arm 17 extends substantially tangentially to the bottom of said groove 16. The rejector arm 17 is integral with a wall 22 delimiting the holding space 21 for storing the ribbon 4. The aforementioned lateral edge 15 of the supporting protrusion 8 is substantially aligned with a bend in the supporting wall 9 which supports the supporting protrusion 8 at a raised height above the bottom wall 10 of the bottom half 2. Said supporting wall 9 is integral with and perpendicular to the bottom wall 10 of the bottom half 2 and has a curved shape following partially the circumference of the first driving gear 6. That allows the supporting protrusion 8 to be embodied as a thin web, since the self-supporting length of the supporting protrusion 8 between the arcuate recess 11 and the supporting wall 9 is short, so that the load applied by the first driving gear 6 on the recess 11 results only in a small leverage. Thus, the bearing means 8 for supporting the first driving gear 6 is compact and light. Referring now to figures 5, 7 and 9, which show the bottom half 2 of the housing 1 in a bottom and top view, it can be seen that the bottom half 2 is provided with a first opening 19 in the bottom wall 10 below the supporting protrusion 8, which first opening 19 is shaped essentially correspondingly to the shape of the supporting protrusion 8. Since the bottom half 2 of the housing 1 (and also the top half 3) is moulded, preferably made of plastic, the supporting protrusion 8 can be moulded in one piece with the bottom half 2 by means of a simple and thereby cheap mould without a movable core. Additionally, the bottom half 2 is in a similiar way provided with a second opening 20 which is formed in the bottom wall 10 below the rejector arm 17 and which is shaped as a slot, correspondingly to the shape of the rejector arm 17. Owing to said second opening 20, the rejector arm 17 can also be moulded in one piece with the bottom half 2 by means of a mould without a movable core. A lower half of the mould for the bottom half 2 of the housing 1 needs therefore only a protrusion extending through the bottom wall 10 to mould the rejector arm 17 and the supporting protrusion 8, respectively. As may be best seen in figures 11 to 15, the top half 3 of the housing 1 is provided with positioning pins 26 which fit into corresponding positioning holes 27 provided in the bottom half 2 of the housing 1 as may be best seen in figures 6 to 9. These positioning holes 27 are formed in side walls 22 delimiting the essentially tub shaped bottom half 2. The positioning pins 26 are integrally formed with the top half 3 and snuggly fit into the corresponding positioning holes 27, so that the bottom half 2 and the top half 3 are connected to each other by means of these positioning pins 26 and positioning holes 27 which moreover position the top half 3 and the bottom half 2 exactly relative to each other. That is imporatant because the second driving gear 5 is supported by both the top half 3 and the bottom half 2, so that an inaccurate position of the top half 3 relative to the bottom half 2 would result in the axis of rotation of the second driving gear 5 being inclined. With the ribbon cartridge having the driving means structure according to the present invention, a simple and reliable transport of the ribbon is achieved, which driving means structure prevents the ribbon from being folded or twisted, as it does not climb or slide towards the top and bottom half of the housing, respectively, in particular because of the self-alignment of the first driving gear with the second driving gear.

Claims: A ribbon cartridge comprising a housing (1) having a bottom half (2) and a top half (3), a ribbon (4) received in said housing (1), a driving means (7) for driving said ribbon (4), said driving means (7) having a first cylindrical driving gear (6) and a second cylindrical driving gear (5), both being rotatably supported in said housing (1), said first driving gear (6) being driven by said second driving gear, said driving gears (5,6) being in engagement with each other for transporting the ribbon (4) between said driving gears (5,6), bearing means (8) for supporting the first driving gear (6) at a circumferential groove (12) in the middle of its height to allow self-alignment of said driving gear (6) with the second driving gear (5) by adjustment movements other than a rotation around the axis of rotation, characterised in that said bearing means (8) is integrally formed with the bottom half (2) of the housing (1) while a self-alignment clearance is provided between the bearing means (8) and the first driving gear (6). A ribbon cartridge as claimed in claim 1, characterised in that said bearing means is a supporting protrusion (8) extending towards said first driving gear (6) in parallel with a bottom wall (10) of said bottom half (2) at a certain height thereabove and having an arcuate recess (11) receiving said first driving gear (6). A ribbon cartridge as claimed in claim 2, characterised in that said supporting protrusion (8) extends from a supporting wall (9) which is integral with and perpendicular to the bottom wall (10) of said bottom half (9) and has a curved shape following partially the circumference of the first driving gear (6). A ribbon cartridge as claimed in claim 2 or 3, characterised in that the first driving gear (6) is provided with a circumferential groove (12), the centre shaft (24) of which is in engagement with said supporting protrusion (8). A ribbon cartridge as claimed in at least one of claims 2 to 4, characterised in that the portion (13) of the supporting protrusion (8) delimiting the arcuate recess (11) has a thickness in axial direction greater than the thickness of a body portion (14) of said supporting protrusion (8), clearance being provided between the supporting protrusion (8) and the groove (12). A ribbon cartridge as claimed in at least one of claims 1 to 5, characterised in that a rejector finger (15) extends essentially tangentially to the circumference of the first driving gear (6) to prevent the ribbon (4) from coiling around said first driving gear (6). A ribbon cartridge as claimed in claim 6, characterised in that a lateral edge (15) of said supporting protrusion (8) serves as rejector finger and extends essentially tangentially to the circumference of said first driving gear (6). A ribbon cartridge as claimed in at least one of claims 1 to 7, characterised in that the second driving gear (5) is rotatably supported by the bottom half (2) and the top half (3) of the housing (1), said second driving gear (5) being provided with at least one protrusion co-axially with its axis of rotation to engage with a recess or opening in the bottom (2) and/or the top half (3), or the bottom half (2) and/or the top half (3) being provided with a protrusion to engage with a recess co-axially with the axis of rotation of said second driving gear (5). A ribbon cartridge as claimed in claim 8, characterised in that the second driving gear (5) is provided with a turning knob (18) extending through a hole in the top half (3) of the housing (1). A ribbon cartridge as claimed in at least one of claims 1 to 9, characterised in that a rejector arm (17) extends essentially tangentially to the circumference of the second driving gear (5) to prevent the ribbon from coiling around said second driving gear (5). A ribbon cartridge as claimed in claim 10, characterised in that a second driving gear (5) is provided with a circumferential groove (16) from which the rejector arm (17) integrally formed with the bottom half (2) of the housing (1) extends substantially tangentially to the bottom of said groove (16). A ribbon cartridge as claimed in at least on of claims 1 to 11, characterised in that a first opening (19) is formed in the bottom wall (10) of the bottom half (2) below the supporting protrusion (8), said first opening (19) being shaped correspondingly to the shape of the supporting protrusion (8) to allow molding of the protrusion (8) without use of a core. A ribbon cartridge as claimed in at least one of claims 1 to 12, characterised in that a second opening (20) is formed in the bottom wall (10) of the bottom half (2) below the rejector arm (17), said second opening (20) being shaped correspondingly to the shape of the rejector arm (17). A ribbon cartridge as claimed in at least one of claims 1 to 13, characterised in that the top half (3) and the bottom half (2) of the housing (1) are provided with positioning pins (26) and/or positioning holes (27) for connecting and positioning the top half (3) and the bottom half (2) relative to each other. A ribbon cartridge as claimed in at least one of claims 1 to 14, characterised in that the positioning pins (26) are integrally formed with the top half (3).

Inventors: YEONG WONG CHYN, YEONG, WONG CHYN
Applicants: FULLMARK PTE LTD
Application year: 1994
Main classification: B41J33
IPC codes: B41J32, B41J33